For most creatures, survival depends on the battle for resources; whether it’s food, shelter or territory. But could temperature be another resource that cold-blooded (ectothermic) creatures are prepared to compete over? At high temperatures the metabolism of warm ectotherms runs faster, allowing them to be more active while requiring more fuel, whereas less active cooler ectotherms will dine less but may have more energy to devote to growth. Well known for their aggression and for establishing dominance hierarchies, crayfish depend on their surroundings to maintain their body temperature, so scientists from Brock University, Canada, led by Glenn Tattersall and Joffre Mercier, decided to find out whether crayfish were prepared to fight over a location that provides the optimal temperature (p. 1892).
Building a crayfish arena divided into two halves, where each half could be maintained at a different temperature by its own computer-controlled coffee machine, Tattersall teamed up with Joshua Luebbert and Kiel Ormerod to test the crustaceans’ temperature preferences. First, they established the crayfish’s preferred temperature by slowly altering the temperature in one chamber and allowing individuals to move between the arena chambers to select their preferred temperature. Next, they paired juvenile crayfish together for 3 days to establish and cement their relationship. Then, they offered the crustaceans a choice between a chamber at their preferred temperature and a second chamber that was well outside their comfort zone and either 4°C warmer or cooler than the first.
Monitoring the crayfish, the duo realised that there were hardly any aggressive interactions between the two animals. On occasions, the crayfish managed to share the preferred temperature chamber; however, the dominant animal established itself in possession of the comfortable chamber almost half of the time with the subordinate crayfish readily backing down to make do with the hot or cold alternative. ‘The established hierarchy did not exhibit conflict over the preferred temperature’, says Tattersall.
However, when Tattersall and Olivia LePine repeated the experiments with crayfish that had only just been introduced to one another, it was a different story. This time, despite establishing their relative status within half an hour, the subordinate crayfish continued challenging the dominant inhabitant for access to the preferred temperature chamber.
So, crayfish are prepared to fight to gain access to locations where the temperature best matches their lifestyle and they resolve their battles differently, depending on their social history. Tattersall says, ‘Being too warm appears to be a condition that forces them to fight more during shared bouts at their preferred temperature. Likely, the warm temperatures are perceived as thermally more stressful than cold temperatures’.